measuring distance with axis camera

[windtakers]

I've read many different post on measuring the distance of you robot to the hoop and different pdfs like this, but their are a few things I don't understand.

1) How do you account for the rectangle distortion when you are not directly in front of it and at a downward angle.

2)how accurate can I get the distance measurement

3)what is the most accurate way to measure distance with a camera or multiple cameras

4)what would the easiest way to measure distance with a camera.